In conventional drilling or boring of wells a drill string comprises a plurality of drill pipe sections coupled together with a drill bit secured to the lower end of the string. As additional drill pipe sections are to be added to the length of the drill string, the uppermost pipe section in the string is held stationary while the additional section of drill pipe is rotated and threadably secured to the uppermost section.
Typically this procedure involves the use of a rotary table which is supported in a horizontal plane. The drill pipe passes through an opening in the center of the rotary table.
To uncouple the drill pipe sections a reverse procedure is used. As the drill string is raised out of the bore hole individual drill pipe sections are unthreaded and removed. The drill bit is then detached from the lowest drill pipe section.
In conventional drilling rigs used for wells deeper than about 3000 feet the rotary table is very large. The opening in the center of the rotary table is sufficiently large that the drill bit on the lower end of the drill string is able to pass through the opening.
However, in conventional truck-mounted drilling rigs used for shallow wells (e.g., water wells or oil wells less than about 3000 feet deep), the opening in the rotary table is too small to allow the drill bit to pass through it. Thus, it is necessary to attach or detach the drill bit to or from the lower end of the drill string, respectively, at a point below the rotary table. Normally in this situation the drill bit must be attached, or detached, manually using long pipe wrenches. This is very much labor-consuming and also potentially dangerous.
There have previously been proposed various techniques and apparatus for connecting and disconnecting drill pipe sections in the field. See, for example, U.S. Pat. Nos. 3,239,016; 3,446,284; 3,463,247; 3,552,506; 3,554,298; 3,768,579; 4,057,887; 4,352,399; and 4,495,840. None of such apparatus, however, is suitable for use with a small truck-mounted drilling rig where the opening in the rotary table is smaller than the drill bit.
Rotary tables and other related drilling apparatus are described, for example, in U.S. Pat. Nos. 1,455,142; 1,506,583; 2,054,223; 2,719,025; 3,195,640; 3,739,434; and 4,410,044. However, none of such patents describe apparatus or techniques for safely attaching or detaching, a drill bit to the lower end of a drill string in a small truck- mounted drilling rig.
There has not heretofore been provided apparatus or techniques for solving the problems noted above.